1. Field of the Invention
The present invention is generally in the field of integrated circuits and, specifically, the invention is in the field of fuse based One Time Programmable (OTP) ROMs or PROMs.
2. Prior Art
Fuse based Programmable Read Only Memories (PROMs) were common up until the 80's when they were largely replaced by UV erasable EPROMs. For example, in U.S. Pat. No. 4,701,695 a metal fuse based PROM is shown in which an NPN bipolar transistor is used to select a fuse in an array of fuses. The fuse is blown or opened with about 50 mA of current at a voltage of 3V. The term program refers to changing the electrical resistive state of fuses in a PROM array to be representative of a desired bit pattern.
There is, however, a need to embed some amount of programmable read only memory in standard CMOS circuits. The PROM can be used to encode configuration information, date codes, serial numbers, etc. Ideally, the programmable memory or PROM can be made in a generic CMOS process without adding any additional processing steps for the PROM.